[kcmkwin/rules] Disable detect button on Wayland

Summary:
The detect functionality is still extremely bound to X11 and results in
a crash when clicked. Thus it's better to disable it completely in 5.12
on Wayland.

Test Plan: Button disabled on Wayland, enabled on X11

Reviewers: KWin, Plasma

Subscribers: plasma-devel, kwin

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D10642